1. Field of the invention
The present invention relates to a sewing machine and more particularly related to a sewing machine having a device for adjusting a pressure normally applied to a presser bar and a device for reducing the pressure when the presser bar is lifted, the devices being operated easily and smoothly.
2. Prior Art
Generally a sewing machine is provided with a presser bar having a presser foot removably mounted to the lower end thereof The presser bar is normally arranged under a downward pressure of a spring and may be vertically movable between an upper inoperative position where the presser foot is spaced from a cloth placed on a needle plate to be stitched and a lower operative position where the presser foot is pressed against the cloth so that stitches may be formed on the cloth. Generally the spring has a strong pressing force and the presser bar is normally lifted from the lower operative position to the upper inoperative position by operation of a lever against the strong pressing force of the spring. Further the pressing force is adjusted generally by loosening or fastening a screw which is in engagement with a top of the spring.
The cloth to be stitched may be different in type and thickness. Particular it is required to press a thick cloth or a leather against the needle plate with a comparatively strong pressure. It is, therefore, required to lift the presser bar against such strong pressure electrically or manually by operation of the presser bar lifting lever.
However, in case the presser bar lifting lever is operated to move up the presser bar, the strong pressure of the spring gives a heavy load to the members forming the transmission mechanism causing abrasion between the members of the transmission mechanism. This will detract a smooth operation for lifting the presser bar and shorten the working life of the mechanism.
The invention has been provided to eliminate the defects and disadvantages of the prior art. It is, therefore, a primary object of the invention to a sewing machine with a device for adjusting a pressure normally applied to a presser bar and a device for lifting the presser bar.
It is another object of the invention to operate devices which are compact in mechanism and smooth in operation.
It is another object of the invention to reduce the pressure normally applied to the presser bar when the presser bar is lifted.
The other objects and advantages of the invention will be apparent from the detailed description of the invention.
In order to attain the objects, the sewing machine of the invention comprises a presser bar supported on a machine frame and being vertically movable with a presser foot removably mounted to the lower end thereof, a spring normally giving a downward pressing force to the presser bar, a swingable member swingably supported on the machine frame and having one end engaging the spring and the opposite end engaging a positioning member which is operated to swing the swingable member to displace the one end thereof with respect to the spring to adjust the pressing force of the spring to the presser bar, thereby to adjust the pressing force of the spring applied to the presser foot which is pressed against a work placed on a needle plate to be stitched.
In a preferred embodiment, the swingable member is operated by a drive device including a pulse motor. Means for selecting a pressure applied to the presser bar may be provided to operate the swingable member. In case an embroidery pattern is stitched, an embroidery pattern may be optionally selected with simultaneous selection of a pressure to be applied to the presser bar which is most suitable to the selected pattern.
Further the sewing machine of the invention comprises a presser bar supported on a machine frame and being vertically movable with a presser foot removably mounted to the lower end thereof, a spring normally giving a downward pressing force to the presser bar, a swingable member swingably supported on the machine frame and having one end engaging the spring and the opposite end engaging a positioning member which is operated to swing the swingable member to displace the one end thereof with respect to the spring to adjust the pressing force of the spring to the presser bar, presser bar lifting means for moving up the presser bar, wherein the positioning member being operated in association with operation of the presser bar lifting means to swing the swingable member to displace the one end thereof with respect to the spring to nullify the pressing force of the spring to the presser bar, thereby to reduce the pressing force of the spring applied to the presser bar when the presser bar is lifted.
The presser bar lifting operation and nullification of the spring action may be made by a mechanism which is operated by a pulse motor. Further, the presser bar may be lifted by manual operation and the spring action may be nullified by the mechanism which is operated by a pulse motor. The manual operation may include the operation by hand or by knee.